People with myopia always need to wear glasses or corrective lenses that enable light rays to be focused on the retina. If not corrected properly, short-sightedness may lead to various difficulties when performing daily activities:
- blurred vision when walking down the street, with difficulty recognizing distant people, objects, and signs;
- general focusing, with a tendency to squint and frown to see more clearly;
- headaches and blurred vision, with pain in the forehead or temples caused by visual fatigue;
- a further decrease in visual acuity may be perceived during twilight or at night.
For people with myopia, light rays from distant objects focus in front of the retina instead of directly on it — as happens in emmetropia — and then diverge, resulting in a blurred image.
Myopia is the most common visual defect in the world, affecting about ¼ of Italians and up to ⅘ of Asians.
Genetic predisposition is one of the main causes of high myopia, which is closely related to physical development. In most cases, onset is detected during school age, with a tendency to worsen during development and stabilize around 20–25 years of age.
In addition to genetic predisposition, recent studies have shown that high myopia may also be due to incorrect behaviours.
New scientific evidence shows that short-sightedness may be induced by poor behaviour such as prolonged effort, for example, reading in low light or holding texts too close to the face.
Even people who read for long periods of time or do precision work may acquire a high degree of short-sightedness, which can even progress after the age of 30.
Myopia is measured in diopters generally calculated on a decimal scale. For example, a deficit of 4 diopters means that a myopic person can read letters at a distance of 6 meters that people with normal vision would be able to read from 10 meters.
Mild myopia is defined as a defect of 3–4 diopters or less.
Medium or medium-strong myopia is defined as a defect of up to 8–9 diopters.
High myopia is defined as any defect greater than 9 diopters.
Myopia is normally due to excessive eye length or excessive curvature of the cornea or lens, conditions that prevent the normal convergence of light rays on the retina.
These vision defects are remedied with corrective lenses or surgery, depending on the specific case.
According to recent studies, children who spend more time outdoors have a lower tendency to develop myopia, since the eyes benefit from natural light and adapting to see distant objects. It is essential that proper correction be used right from the start to prevent any defects from becoming more pronounced.